In order to survey one target point or, in particular, a plurality of target points, numerous geodetic survey devices have been known since antiquity. Here, distance and direction or angle from a surveying device, the absolute position of which is known, to the target point to be surveyed are recorded as spatial standard data. Well-known modern examples of such geodetic surveying devices are tachymeters and total stations, which are also referred to as electronic tachymeter or computer tachymeter. A geodetic surveying device from the prior art is described in e.g. EP 1 686 350.
It is often the case that the target point, e.g. a boundary marker, cannot be directly targeted by the surveying device due to obstacles which interrupt the line of sight. Hence, points are surveyed in a number of geodetic applications by virtue of specially embodied target objects being placed thereon. According to the prior art, these consist of a rod as object support with a marking that can be targeted or with a retroreflector as target object. For surveying purposes, the tip of this plumb rod with the target point is brought into contact with the ground and held perpendicular to determine the direction. In so doing, in order to determine the distance, the rod will be aligned horizontally in such a way by rotating it about its vertical axis that the marking or the reflector reflects a light signal emitted by the surveying device back in the direction of the latter. Alternatively, use is made of 360° reflectors, which reflect light signals back from any horizontal alignment. This procedure requires two users: one to operate the surveying device and one to place and hold the target object.
In order to enable geodetic surveying by a user on his own, total stations according to the prior art have means for mechanizing the target optical unit, for automated target search and tracking and for remote control of the whole device, as a result of which measurements can be performed by means of a suitable remote control unit from the target point. Modern total stations moreover contain microprocessors for digital further processing and storing of registered measurement data and a radio data interface for establishing a radio connection to external peripheral components such as e.g. a data-registering device, which can be embodied as a field computer in particular. By means of the data interface, it is possible to emit measurement data registered and stored by the total station for external further processing, to read externally registered measurement data into the total station for storage and/or further processing and to input or output remote control signals for remotely controlling the total station or a further external component, particularly in mobile field use. Modern devices can have a camera, for registering an image, aligned in a target direction, wherein the registered image in particular can be displayed as live image on the display of the display/control unit and/or on a display of the peripheral device used for the remote control, such as e.g. a field computer.
Here, a target reflector can be targeted by means of, in particular, this live image displayed to the user in the display of the remote control unit. Accordingly, the user can correspondingly align the total station on the desired target that can be identified in the live image on the basis of the live image.
In the prior art, appropriate peripheral devices suitable for remote control have radio data interfaces for wireless communication and data transfer with the total station or other external devices and control units with appropriate control software. Received data can be evaluated by means of an evaluation unit and displayed to the user by means of an output means, e.g. an electronic display. Furthermore, the user can communicate with the remote control unit and, thereby, with the surveying device by means of input means such as e.g. a keyboard or a touch-sensitive display. Hence, the user is able to initialize and perform measurements from the target point to be surveyed, and to register the results thereof. By storage in the total station, the field controller or an external memory, access to data is possible at a later time. Examples of such devices are the field controllers CS10 and CS15 by Leica Geosystems.
A one-person measurement system is obtained from the combination of geodetic surveying device, remote control unit and target object support. In this case, the target object support is usually also used as support for the remote control unit, i.e. the field controller can be attached to the plumb rod by means of an appropriate holder.
In general, a disadvantage of using such a rod for geodetic surveying is that conveying and carrying a rod, which is generally more than two meters long and therefore unwieldy, is cumbersome to the user and laborious in terrain that is difficult to pass, e.g. a wooded area. Moreover, perpendicular set up of the rod is connected to a certain amount of time expenditure and perpendicular holding during the measurement is arduous for the user. Incorrect setup of the rod at the target point is a source of error for an incorrect determination of position. A further disadvantage is that target points in a geodetic survey could lie in such a way that perpendicular positioning of the rod on the target point is impossible or that it is even impossible to establish physical contact, e.g. if the target point is a corner of a building, if visual obstacles, e.g. bushes and trees, are present between the total station and the target object or if the surroundings of the target point cannot be entered by the user. Such situations require specific measurement methods, which are connected to additional time expenditure.
U.S. Pat. No. 6,381,006 B1 discloses a method and a corresponding device, by means of which surveying of inaccessible target points is possible. To this end, a plumb rod is equipped with at least two sensor elements, the absolute positions of which are determined by means of one or more reference stations, e.g. a geodetic surveying device. Furthermore, the plumb rod has a distance-measuring device, which measures the distance between distance-measuring device and a target point to be surveyed. The positions of the sensor elements and of the distance-measuring device relative to one another and the orientation of the distance-measuring direction are known. Hence, it is possible to calculate the absolute position of a target point from the measured distance and the measured absolute positions of the sensor elements.
However, this method does not avoid the above-described disadvantages connected with the use of a plumb rod. Furthermore, it is disadvantageous that at least two sensor elements are required for determining the absolute position, which moreover must have a certain minimum distance between one another for sufficient resolution accuracy. As a result, the plumb rod becomes even more unwieldy, which is also indicated by the remark in U.S. Pat. No. 6,381,006 B1 that, preferably, attention is paid to a balanced arrangement of the components in respect of weight distribution.
U.S. Pat. No. 5,903,235 discloses a geodetic surveying device that can be hand-held, with which surveying can be performed without use of a geodetic surveying device having a distance and direction measurement functionality and without use of a plumb rod. Here, the target point to be surveyed is targeted by a pointing unit, e.g. a laser pointer. The position of the surveying device relative to the target point is established firstly by measuring the distance between device and target point in a defined direction by means of an integrated distance-measuring unit. In so doing, there is no need to align the device perpendicularly over the target point since a component which determines the inclination relative to the gravity vector is integrated. The absolute position of the surveying device is determined by a GNSS reception unit, as a result of which it is ultimately possible to calculate the absolute position of the target point due to the preceding measurements. Thus, handling of a plumb rod is dispensed with and it is possible to survey target points that could not be contacted physically by a plumb rod.
However, even when using correction signals, GNSS-based systems only enable a less accurate determination of the position of target points than systems based on the use of the distance and direction measurement functionality of a corresponding geodetic surveying device. Moreover, determining the position is bound to receiving a sufficient number of GNSS signals, which is not always the case, e.g. when tunneling or in narrow road lines.